Only people with tumors that test positive for ALK — about 3 to 5 percent of NSCLC patients, or around 6,500 to 11,000 U.S. patients a year — are candidates for the treatment. By comparison, last year more than 45 million prescriptions were dispensed for Lipitor, the cholesterol-fighter that is Pfizer's biggest seller.

The FDA approved the pill in combination with a genetic test to detect the ALK variation to figure out who has the best chance of responding to the medicine.

The new, highly targeted cancer pill won't come cheap at about $9,600 a month. But the benefits for those with the ALK-positive cancers appear to be substantial. Half or more of patients in the studies cited in the FDA approval responded well to treatment with Xalkori. Their tumors shrank or disappeared.

But there are no definitive data so far on whether the drug extends life, though that's expected to be the case. The FDA approved the drug quickly, under a priority review approach reserved for drugs that have special promise. Pfizer has to perform more studies of the drug to confirm the agency's assessment of Xalkori.

Common side effects from Xalkori include vision problems, nausea and diarrhea. More rarely, in less than 2 percent of cases, patients experienced life-threatening inflammation of the lungs.

One high-profile patient who took Xalkori in clinical trials is former Microsoft engineer Andy Hill, a state senator in Washington. Diagnosed with NSCLC in early 2009, he started taking the pill in October of that year. Since Feb. 2010, he's shown no signs of lung cancer. "It's pretty miraculous," he told the Redmond Reporter. "I am doing things I never thought I would ever be able to do again."

For more on Hill's case and how cancer patients can make the best use of the Internet and medical professionals in making treatment decisions, watch the video below of Dr. Jack West, a lung cancer specialist at Seattle's Swedish Medical Center. (Hat tip on video to Sally Church at Icarus Consulting.)